There has been increasing demand for optical modules with higher optical output to use as light sources or for processing applications.
The operating lifetime of a light source (e.g., a laser diode) is dependent on, among other things, its operating temperature. A high quality light source, operating at 20° C., could have a lifetime in excess of 100,000 hours. However, as the optical power of the light source increases, the amount of heat generated by the light source also increases, and dissipating this heat can present significant technical challenges to the designer, particularly where the optical module is used in an optical module array assembly where a sizable number of optical modules must be packaged in a relatively confined space.
Failure of a light source is defined as the point in time when the operating current required to maintain a specified output power is increased by some percentage (e.g., 50%) of the original operating current. The output power of a light source is usually measured by a monitor photodiode integrated into the optical module which houses the light source. However, not all optical modules have monitor photodiodes incorporated therein, so the risk of the light source overheating and failing without appropriate detection is substantial.
This “excessive heat” issue is further compounded by the continuous release of new light sources with higher output powers from light source manufacturers, and the placement of high power optical modules in close proximity to each other so as to form dense arrays in optical module array assemblies.
To maximize the optical source lifetimes, and to ensure reliable operation of optical modules, it is necessary to provide adequate heat sinking for the optical module and, in particular, for the light source contained in the optical module.
However, optical modules installed in a heat sink have traditionally been difficult to remove and replace. It would, therefore, be highly beneficial to the user if a defective optical module in an optical module array assembly (having a heat sink) could be easily removed and replaced in the field by a non-technical person in a short period of time without the need for special tools.
In addition to the foregoing, optical modules require associated electronics, generally in the form of a printed circuit board (PCB), to drive the light source in the optical module. In some cases, an internal PCB is incorporated in each optical module. More commonly, however, optical modules are supplied independently of a PCB, and the optical modules are connected to an external PCB. This approach is particularly popular for optical module array assemblies. In this case, all of the optical modules of the optical module array assembly may be driven by a single external PCB. Each optical module plugs into the external PCB via the back end of the optical source of that optical module. As old optical modules become defective, replacement optical modules can simply be plugged into the existing PCB, leading to significant cost savings. The heat sink typically sits substantially parallel to the PCB, with the optical modules extending through, and mounting to, the heat sink.
It is important that the optical module plugs into the external PCB correctly. For example, when a optical module having a laser diode is mounted in a heat sink, the laser diode (within the optical module) must be correctly connected to the PCB (i.e., the positive pin of the laser diode must connect to the positive connector of the PCB, and the ground pin of the laser diode must connect to the ground connector of the PCB). Failure to do so results in malfunction of the laser diode and permanent damage to the laser diode when a voltage is applied.
Therefore, it would also be beneficial to provide a heat sink design suitable for a range of different sizes of optical module array assemblies that allows for easy replacement of defective optical modules and includes features to ensure the proper orientation of the optical modules relative to the PCB for correct electrical connection.